This invention relates to a gas generator, such as a hydrogen generator, particularly a gas generator with a gas flow valve that also functions as a pressure relief valve.
Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
There are several types of fuel cells, each using a different chemistry. Fuel cells can be categorized according to the type of electrolyte used, typically one of five types: proton exchange membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric-acid fuel cell (PAFC), solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC). Each of these types of fuel cell uses hydrogen and oxygen. Hydrogen is oxidized at the negative electrode, and oxygen is reduced at the positive electrode. Ions pass through an electrically nonconductive, ion permeable separator and electrons pass through an external circuit to provide an electric current.
In some types of hydrogen fuel cells, hydrogen is formed from a hydrogen-containing fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell.
A fuel cell system can include a fuel cell battery, including one or more fuel cells (a fuel cell stack), and a gas source, such as a gas tank or a gas generator. Gas generators that supply gas to a fuel cell can be an integral part of a fuel cell system, or they can be removably coupled to the fuel cell system. A removable gas generator can be replaced with another one when the gas producing reactants have been consumed. Removable gas generators can be disposable (intended for only a one-time use) or refillable (intended for use multiple times) to replace consumed reactant materials.
It is desirable for removable gas generators to be easily coupled to the fuel cell system to create a gas flow path from the gas generator to the remainder of the fuel cell system without gas leaks at the coupling, and it is also desirable for the gas generator to be free of gas leaks when not coupled to the remainder of the fuel cell system. The coupling between the gas generator and the rest of the fuel cell system can include one or more valves. The valve(s) can be opened and closed manually, valve operation can be controlled by a control system, or the valve(s) can be opened and closed by an actuator that is operated by making or separating components of the coupling. The latter method can be used in quick disconnect couplings, for example, where the valve is opened when the gas generator is coupled to the rest of the system and closed when the gas generator is uncoupled.
Because the gas generator can contain gas under pressure, it may be desirable to provide means for relieving internal pressure before it becomes high enough to rupture the gas generator housing. A pressure relief vent can be incorporated into the gas generator for this purpose. Examples of pressure relief vents are found in U.S. Patent Publication No. 2006/0174951 A1, in which the pressure relief vent is located in a portion of the gas generator housing, and in U.S. Patent Publication No. 2008/0169207 A1, in which the pressure relief vent is incorporated into a valve assembly that also controls the flow of gas from the hydrogen generator.
Another example of a pressure relief vent incorporated into the valve assembly is found in U.S. Patent Publication No. 2005/0162122 A1. In this valve assembly, if the internal pressure reaches a predetermined level when the gas generator is not coupled to the rest of the fuel cell system, a burst disk opens to relieve the pressure. Gas is released through a portion of the same conduit through which gas flows when the gas generator is coupled to the rest of the fuel cell system.
An object of the present invention is to provide a gas generator that can be reliably sealed to prevent gas leaks when coupled to or uncoupled from a from a fuel cell system and that can provide a pressure relief vent when the gas generator is uncoupled.